Electrode mount



May 3, 1938. N. R. SMITH ELECTRODE MOUNT Filed Dec. 51, 1936 INVENTOR NEWELL R. SMITH V %C ATTORN EY Patented May 3, 1938 UNITED STATES PATENT OFFICE mesne assignments,

to Radio Corporation of America, a corporation of Delaware Application December 31, 1936, Serial No. 118,523

Claims.

My invention relates to electron discharge devices, particularly to electrode constructions and their mount assemblies.

Minimum spacing of electrodes of a mount in I a tube with the usual tensioned filamentary cathode is limited by the room required for the cathode which, because of its flexibility, is free intermediate its ends to vibrate and to move considerable distances. In power rectifiers, for example, it is important that the anode cathode spacing be as small as possible to minimize the space impedance and permit greater anode current for a given anode operating temperature. Mounts employing the usual filament supporting means are difflcult to-assemble, particular pains being necessary to obtain a fixed and uniform spacing between the filament and surrounding electrodes.

An object of my invention is to provide a mount with a filamentary cathode and cooperating elecso trodes that may be easilyassembled.

A further object of my invention is to provide a mount with an anode and rigid self-sustaining filamentary cathode that may be closely mounted in cooperating relation.

28 A further and more specific object 01' my invention is to so form afilamentary cathode with a'cross sectional configuration that may lend sufficient rigidity to the cathode to prevent its vibration or movement between its points of support.

According to my invention, a filamentary cathode and cooperating electrodes are so made that they may be mounted in close spaced relationship, the filamentary cathode being stiffened to make it self-sustaining in its supports, and the anode being so formed about the cathode to increase the tube perviance. Ribbon-like strips of cathode material maybe longitudinally grooved by rolling or pressing, and the channelled filament so constructed out to the proper length and mounted in an electrode assembly. I have, according to one embodiment of my invention, bent the channelled strip at its center to form a 5 V, and welded the ends of the legs of the V" to supporting lead-in wires in the press at the lower end of the tube so that the bight or apex of the filament lightly engages at its edges, the edges of a narrow slot in the upper insulating spacer. V

The characteristic features of this invention are defined with particularity in the appended claims and preferred embodiments are described in the following specification and attached drawing in which;

Figure 1 is a sectioned perspective view of one electrode assembly embodying my invention,

Figure 2 is a detailed view showing the cross sectional configuration of one form of channelled filament constructed according to my invention, and

Figure 3 shows another electrode assembly embodying the characteristic features of my invention.

The electron discharge device shown by way of example in Figure 1 and embodying the characteristic features of my invention comprises an envelope I with a re-entrant stem 2, and press 3 insulatingly supporting the usual lead-in conductors. The tube, chosen for illustration is shown with a glass envelope, although a metal envelope may be used, and with the electrodes of a full wave rectifier comprising anodes 4 secured at their ends to insulating spacers 5 such as mica discs, the entire assembly being supported by the conductors embedded in the press.

Each anode, according to my invention, comprises a single sheet of metal folded as shown with two longitudinal slots or folds 6 extending towards the center of the tube to form indentations facing outwardly, the portions of the anode 1 adjacent the folds being pressed in a cylindrical plane to present to the wall of the envelope a heat radiating surface of considerable area. The walls of the indentations may be accurately formed on a standard punch press machine to uniformly and closely space the sides of the indentation.

A ribbon-like filamentary cathode constructed according to my invention may conveniently be mounted in the slots with a minimum yet accurately fixed-spacing between the walls of the slot and the fiat sides of the cathode. Within each slot is mounted a portion of filamentary cathode 8 shown in detailed section in Figure 2. The filaments, preferably strips of refractory metal such as molybdenum or nickel-iron-cobalt alloy, commercially known as 16 metal, are longitudinally grooved or channelled along the center of the ribbon or strip by-rolling or pressing to form the strip with any desired cross sectional configuration. While the rectangular channel 9 shown in Figure 2 has been found to stiffen the strip sufficiently, the strip may be formed with any other desired cross sectional contour such for example as a semi-circle. In the particular embodiment illustrated in Figure 1 each channelled filament is coated with an electron emitting coating such as barium-strontium-carbonate, is bent to form an inverted U, the legs of the filament inserted in openings or notches in the upper insulating spacer, and their lower ends attached by welding to current supply conductors with the transverse section at the top of the "U" bearing against the upper insulating spacer S to transversally support it.

With the open sided slots in the anode and the stiff filamentary cathode of my invention, the electrodes may be automatically assembled by machines, eliminating the usual hand operations. A chuck, for example, may be inserted through the open side of the slot to guide the filament into place where it is welded, at its lower end, to current supply conductors. It has been found that a filament constructed and mounted as shown in Figures 1 and 2 is self-sustaining, requires no sprlng tensiouing means, commonly accepted as being indispensable for filamentary cathodes, and is rigidly held in place by the two welds at the lead-in wires. The parallel faces of the ribbon-like filament and walls of the slots minimize the anode-cathode impedance of the tube and with the plane of the filament normal to the wall of the envelope electrostatic influences on the cathode. such as "grid efl'ec noticeable particularly in tubes with metal envelopes, is materially reduced. This construction is strikingly simple when compared with the usual mount of this type, is easy to assemble, and inexpensive to manufacture.

My filament has been successfully employed in a commercial tube known as the "80" when the ribbon filament is bent at its center to form a V", as shown in Figure 3, the ends of its legs welded to lead-in conductors l and its apex slidably held at the edges of the strip in opening it in the insulating spacer. Any desired arrangement of grids could. of course, be placed between the anode and cathode. The upper end of the filament is free to slide through the opening when the filament changes in length due to heating, the edge-to-edge contact between the filament strip and mica spacer offering minimum frictional resistance to the movement of the filament. With the ends of the legs of the V-type filament anchored, its apex is free to move only in the plane of the filament legs and the edge-to-edge contact between the filament and spacer ofiers maximum resistance to the flow of heat from the filament to the spacer. In manufacture it may be found desirable to stamp out the upper insulating spacer 5 with a transverse portion or bridge across the center of openings II to underlie that portion of the filament extending above the surface of the upper insulaton, With the spacer so constructed, the apex of the filament above the spacer may be flattened to rest upon the bridge. Such a bridge would serve to prevent the apex of the filament from slipping through the opening and disengaging the spacer.

Since many modifications may be made in this invention without departing from the spirit thereof, it is desired that this invention be limited only by the prior art and the appended claims.

I claim:

1. Anelectron discharge device comprising an envelope, an anode in said envelope with a cylindrical surface concentric with the wall of the envelope and two elongated indentations extending lengthwise of said anode with the sides of said indentations opening in the cylindrical surface of the anode facing said envelope, and a U-shaped filament of ribbon-like refractory metal, the legs of said filament being insulatingly supported in the indentations with the plane of the ribbonlike filament parallel to the walls of the slots.

2. An electron discharge device comprising an anode and a filamentary cathode, an insulating spacer, the anode and cathode insulatingly held in cooperating spaced relation, and the cathode comprising a strip of refractory metal stiffened throughout its length with a longitudinal channel, the lower end of the stiffened cathode strip bemg fixed and the other end of the strip being free to move longitudinally and slidably guided by said insulating spacer.

3. An electron discharge device comprising an envelope, an anode in said envelope comprising a metal sheet, said sheet being folded to form an elongated indentation, the sides of said indentation opening upon the wall of said envelope, an

insulating spacer, a ribbon-like cathode of refractory metal, longitudinally grooved to stiflen the cathode, secured in and spaced from the sides of said indentation, one end of the cathode ribbon being fixed and the other end of the ribbon being slidably guided by said insulating spacer.

4. An electron discharge device comprising an anode and a filamentary cathode, an insulating spacer, the anode and cathode being insulatingly held in co-operating spaced relation said cathode comprising a ribbon of refractory metal stiflened throughout its length with a longitudinal channel, the width of the channel in said ribbon being substantially less than the width of said ribbon.

5. A cathode for an electron discharge device comprising a straight flat ribbon, a longitudinal channel in said ribbon to stiffen the ribbon, and electron emissive material in said channel.

NEWELL R. SMITH. 

